Add 3.13 to our CI (#11926)

tests/runtests.py

@@ -62,7 +62,7 @@ def main() -> None:
     parser.add_argument(
         "--python-version",
         default=_PYTHON_VERSION,
-        choices=("3.8", "3.9", "3.10", "3.11", "3.12"),
+        choices=("3.8", "3.9", "3.10", "3.11", "3.12", "3.13"),
         help="Target Python version for the test (default: %(default)s).",
     )
     parser.add_argument("path", help="Path of the stub to test in format <folder>/<stub>, from the root of the project.")